Sectional anatomy


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Sectional anatomy

  1. 1. Chapter 2 Face OUTLINE I. Facial Bones A. Maxillary Bones B. Zygomatic Bones C. Lacrimal Bones D. Nasal Bones E. Inferior Nasal Conchae F. Palatine Bones G. Vomer H. Mandible II. Bony Nasal Septum III. Nasal Fossae IV. Orbit V. Eye VI. Paranasal Sinuses VII. CT Images A. Exam 1 1. Coronal Images 2. Axial Images B. Exam 2 1. Coronal Images 2. Axial Images VIII. Review Questions 67
  2. 2. 68 Fundamentals of Sectional Anatomy FACIAL BONES Maxillary Bones Chapter 1 presented the eight cranial bones: the frontal, The two maxillary bones are the largest immovable two parietals, occipital, two temporals, sphenoid, and eth- bones of the face and are solidly united midline inferiorly. moid. In examining CT images for facial bones you again They are involved in forming three cavities: the oral, nasal, encounter some of these same bones as well as the 14 and orbital. The upper teeth are imbedded in the inferior facial bones themselves. The list of facial bones includes margin, the alveolar process or alveolar ridge. Figure the two maxillae, two zygomatic bones, two lacrimal bones, 2-1 demonstrates the maxillary bones from an anterior per- two nasal bones, two nasal conchae, two palatine bones, spective, including the frontal processes articulating with one vomer, and one mandible. the frontal bone. Figure 2-2 shows the inferior horizontal portion of the maxillary bone, the palatine process. It forms the anterior part of the hard palate, or roof of the mouth. Frontal bone Parietal bone Temporal bone Frontal process of maxillary bone Sphenoid bone Nasal bone Ethmoid bone Zygomatic bone Lacrimal bone Middle nasal concha Superior concha Maxilla Perpendicular plate of the ethmoid bone Inferior nasal concha Vomer bone Alveolar process of maxillary bone Alveolar process of mandible Mandible Mentum of mandible Figure 2-1 External frontal view of facial bones
  3. 3. CHAPTER 2 Face 69 Zygomatic Bones Nasal Bones The two zygomatic or malar bones form the promi- The two nasal bones are fused midline and form the nent part of our “cheek bones” and are seen on Figure 2-1. bridge of the nose as seen on Figure 2-1. The zygomatic bones have three points of attachment: anteriorly with the maxillary bone, superiorly with the Inferior Nasal Conchae frontal bone, and posteriorly with the temporal bone. Also demonstrated on Figure 2-1 are the two inferior nasal Trauma may cause them to become free-floating, an injury conchae, or turbinates, which are separate facial bones. called a “tripod” fracture. Palatine Bones Lacrimal Bones Forming the posterior part of the hard palate are the The two lacrimal bones, also seen on Figure 2-1, are two palatine bones. On Figure 2-2, they are seen pos- very tiny bones that help form the medial wall of the terior to the palatine processes of the maxilla. The palatine orbits. They are difficult to distinguish on CT images bones have vertical portions that extend superiorly and are because of their size. minimally involved in forming the orbit. Palatine Hard processes palate of maxilla Horizontal plate Maxilla of palatine bone Zygomatic Vomer arch Temporal Medial bone pterygoid lamina of sphenoid Lateral pterygoid lamina of sphenoid Parietal bone Foramen Occipital magnum bone Figure 2-2 External view of inferior skull
  4. 4. 70 Fundamentals of Sectional Anatomy Vomer the mandible from an anterior perspective and Figure 2-4 The vomer forms the inferior part of the bony nasal demonstrates it from a lateral perspective. The lower teeth septum while the perpendicular plate of the ethmoid bone are rooted in the alveolar ridge or process of the mandible. forms the superior segment. Their relationship is shown on The inferior tip of the mandible is the chin or mentum Figures 2-1 and 2-3. and is identified on Figures 2-1 and 2-4. Also seen on Figure 2-4 is one of the bilateral condyloid processes of the mandible. These processes articulate with the temper- Mandible omandibular fossae of the temporal bones to form the The mandible is the largest facial bone and the only temporomandibular joints. movable bone in the adult skull. Figure 2-1 demonstrates Ethmoid crista galli Frontal bone Ethmoid cribriform plate Sphenoid sella turcica Sphenoid sinus Frontal sinus Sphenoid bone Nasal bone Ethmoid perpendicular plate Septal cartilage Vomer Lateral pterygoid process of sphenoid bone Medial pterygoid process Palatine process of sphenoid bone of maxilla Hamulus Horizontal plate Perpendicular plate of palatine bone of palatine bone Figure 2-3 Midsagittal view of bony nasal septum
  5. 5. CHAPTER 2 Face 71 Frontal bone Parietal bone Temporal bone Sphenoid bone Ethmoid bone Nasal bone Occipital bone Lacrimal bone Temporomandibular joint Zygomatic bone External auditory Condyloid process meatus Maxilla Mastoid process of temporal bone Alveolar process Styloid process of mandible Alveolar process of maxillary bone Mentum of mandible Mandible Figure 2-4 External lateral view of facial bones
  6. 6. 72 Fundamentals of Sectional Anatomy BONY NASAL SEPTUM sagittal line drawing of the nasal septum, and you see both the perpendicular plate of the ethmoid bone and the The nasal septum, the partition separating the two nasal vomer. When studying coronal CT images, the perpendi- fossae, is cartilaginous anteriorly and bony posteriorly. The cular plate of the ethmoid bone is easily differentiated bony nasal septum is actually composed of two separate from the vomer. The separate components of the bony pieces of bone. Superiorly it is formed by the perpendi- nasal septum are more difficult to identify on axial CT cular plate of the ethmoid bone, as pictured from an images. Also easily identified on CT coronal images are the anterior perspective on Figure 2-5. Figure 2-6 places the cribiform plate, the horizontal superior portion of the ethmoid bone with respect to the orbits and nasal cavity. ethmoid bone, and the crista galli, the small superior The inferior portion of the bony nasal septum is a separate extension off the cribiform plate. Figures 2-3, 2-5, and 2-6 facial bone, the vomer. Look back at Figure 2-3, a mid- show these structures. Cribriform plate Crista galli Left Ethmoidal lateral air cells mass Superior nasal concha Middle nasal Perpendicular concha plate Figure 2-5 Frontal view of ethmoid bone Crista galli Cribriform plate Left lateral mass Perpendicular plate Figure 2-6 Ethmoid bone in place
  7. 7. CHAPTER 2 Face 73 NASAL FOSSAE bone. All are visible on Figure 2-7. The orbit is conical in shape, as shown on Figure 2-8, with the widest portion, the The nasal fossae, cavities found on either side of the nasal base, being located anteriorly. When doing coronal CT septum, are broken into compartments by smaller scroll- images, it becomes increasingly smaller as one cuts pos- like bones called conchae or turbinates. There are three teriorly. If someone receives a direct hit in the region of pairs of conchae or turbinates, the superior, middle, and the orbit, the orbit will give in the weakest region, the inferior. The superior and middle conchae are medial floor. This would be termed a “blow-out” fracture. extensions off the two lateral masses of the ethmoid bone. The inferior conchae are separate facial bones. The func- tion of the conchae is to separate the nasal cavity into smaller compartments. When air is inhaled, it is forced to travel through the compartments, and is warmed, filtered Frontal bone by the cilia, and moistened by the mucous membranes lin- Sphenoid ing the nasal cavity. From a coronal perspective, the infe- bone Palatine rior and middle conchae are visible on CT images. The Malar superior conchae are much smaller and may not always be Ethmoid (zygomatic) identifiable. Figure 2-1 labels the conchae. bone bone Lacrimal ORBIT bone There are seven bones involved in forming the orbit. The roof of the orbit is formed by the horizontal portion of the Maxilla frontal bone. The floor is formed by the maxillary bone along the medial aspect and the zygomatic bone along the lateral aspect. The medial wall is formed by the ethmoid and lacrimal bones. The lateral wall is formed by the zygo- Medial Lateral matic bone and posterolaterally by the sphenoid bone. Minimally involved is the vertical portion of the palatine Figure 2-7 The bones of the orbit Apex (optic foramen) 30 Base 37 Figure 2-8 The orbits
  8. 8. 74 Fundamentals of Sectional Anatomy EYE ity exiting the back of the eye. The lens of the eye is also visible on sagittal and axial CT images, but should not be Certain muscles are involved in moving the eye. Those evi- confused with the optic nerve on coronal images, as it is dent on CT images are the superior, inferior, medial (or not visible. It is transparent and convex, allowing light to internal), and lateral (or external) rectus muscles. From a reach the retina, but at the same time causing refraction of coronal perspective you see all four; from an axial per- light. Figure 2-9 demonstrates the medial and lateral rec- spective you see the medial and lateral muscles; and from tus muscles, optic nerve, retina, and lens while Figure 2-10 a sagittal perspective you see the superior and inferior. The shows three of the four rectus muscles. retina is the innermost layer in the posterior eye that con- tains the rods and cones, the nerve cells responsible for vision. The optic nerve exits through the optic foramen in the posterior orbit carrying the sensory information PARANASAL SINUSES received by the retina. The optic nerve is seen on coronal The paranasal or accessory nasal sinuses are air-filled CT images as an area of opacity in the center of the eye. cavities located in some cranial and facial bones. They Looking at axial images, it is visible as a linear area of opac- communicate with the nasal cavity and with each other. Lateral rectus muscle Retina Lens Optic nerve Medial rectus muscle Figure 2-9 Transverse view of the eye Superior oblique Superior rectus Inferior Inferior Lateral oblique rectus rectus Figure 2-10 The muscles of the eye
  9. 9. CHAPTER 2 Face 75 Their function is to lighten the head and add resonance to The sphenoid sinuses are beneath the sella turcica, in the the voice. They are lined with mucous membranes and with body of the sphenoid bone. A septum separates the sphe- pathology can become filled with fluid. Named for the noid sinus from the ethmoid sinuses and an additional bones in which they are located, they are the maxillary, septum exists if there is more than one sphenoid sinus. frontal, ethmoid, and sphenoid. Only the maxillary The sphenoid sinuses are located posterior to the ethmoid sinuses are present at birth. The frontal and sphenoids sinuses, as drawn on Figure 2-11. The frontal sinuses form around the age of 6 or 7, and the last to develop, are the most superior and the maxillary sinuses the most in the late teens, are the ethmoids. The largest are the inferior. Coronal CT images demonstrate that the frontal maxillary sinuses, with one being located in the body of sinuses are the most anterior and the sphenoid sinuses each of the two maxillary bones. The frontal sinuses are in the most posterior. If the orbits are visible on coronal the vertical portion of the frontal bone. There may be cuts, the sinuses you are visualizing are probably the eth- either one or two, with a septum or wall dividing them if moids rather than sphenoids. Figure 2-12 demonstrates two exist. Rarely are they symmetric. The many ethmoid all four paranasal sinuses from a coronal perspective. The sinuses are located within the two lateral masses of the sinuses appear translucent on CT images unless pathology ethmoid bone, found along the medial wall of each orbit. exists. Frontal sinus Ethmoid air cells Maxillary sinus Sphenoid sinus Figure 2-11 Lateral view of paranasal sinuses Frontal sinuses Ethmoid air cells Sphenoid sinuses Maxillary sinuses Figure 2-12 Frontal view of paranasal sinuses
  10. 10. 76 Fundamentals of Sectional Anatomy CT IMAGES Exam 1 Coronal Images Frontal bone Frontal sinus Perpendicular plate of ethmoid bone Nasal bone Frontal process of maxillary bone Figure 2-13 Although Figure 2-13 is not the first image of this exam, it is anterior enough to demonstrate the unusually large but typical asymmetric frontal sinuses.The nasal bones are seen along with the portions of the maxillary bones involved in forming the medial walls of the orbits, the frontal processes. Just starting to appear is the perpen- dicular plate of the ethmoid bone which forms the superior portion of the bony nasal septum. Frontal bone Frontal Superior orbital sinus margin Lacrimal Perpendicular bone plate of ethmoid bone Alveolar process of maxillary bone Figure 2-14 The superior orbital margin, formed by the frontal bone, is evident on Figure 2-14. More of the per- pendicular plate of the ethmoid bone has appeared. The lower edge of the maxillary bone, the alveolar process, is shown. It is here that the upper teeth attach.The lacrimal bones, which help to make up the medial walls of the orbits, are labeled.
  11. 11. CHAPTER 2 Face 77 Crista galli Superior Cribiform plate orbital of ethmoid bone margin Ethmoidal air Lateral mass of cells ethmoid bone Middle nasal Zygoma concha Maxillary Inferior orbital sinus margin Maxillary bone Inferior nasal Vomer concha Mentum of mandible Figure 2-15 Clearly seen on Figure 2-15 is the crista galli extending superiorly from the cribiform plate of the ethmoid bone. Some of the many ethmoidal air cells, found in the lateral mass of the ethmoid bone, have become visible. In addition to the lacrimal bones, the lateral masses of the ethmoid bone help form the medial walls of the orbits. Just starting to appear are the largest of the sinuses, the maxillary sinuses, in the bodies of the maxillary bones. Figure 2-15 also shows the midpoint of the mandible, the mentum, as well as the inferior and middle conchae or turbinates. The inferior conchae, separate facial bones, and the superior and middle conchae extending medially from the lateral masses of the ethmoid bone divide the nasal cavities into compartments. The vomer is seen forming the inferior part of the bony nasal septum. Notice the role the nasal maxillary bones assume in forming the inferior orbital margin. Cribiform plate Ethmoid Superior orbital margin sinus (frontal bone) Lateral mass Crista galli of ethmoid bone Superior nasal Zygomatic concha (malar) bone Middle nasal concha Vomer Maxillary sinus Inferior nasal concha Figure 2-16 Figure 2-16 demonstrates the cribiform plate of the ethmoid bone along with the crista galli. The zygomatic or malar bones are prominent and their involvement in forming the lateral walls of the orbits can be appreciated.
  12. 12. 78 Fundamentals of Sectional Anatomy Optic Superior rectus nerve muscle Lateral Medial rectus rectus muscle muscle Inferior rectus Maxillary muscle sinus Vomer Mandible Figure 2-17 On Figure 2-17, the maxillary sinuses are fully demonstrated, for the most part nonpathologic except for a small area of opacity in the lower right maxillary sinus. A small part of the upper mandible is just starting to appear. Also seen on this coronal image are the four rectus muscles (superior, inferior, lateral, and medial), along with the optic nerve. Cribiform plate Perpendicular of ethmoid bone plate of ethmoid Sphenoid bone bone Middle nasal Maxillary concha sinus Inferior Vomer nasal concha Figure 2-18 Notice the diminished size of the orbits on Figure 2-18, an indication that the image is posterior. The sphenoid bone is seen making up the posterolateral walls of the orbits.
  13. 13. CHAPTER 2 Face 79 Anterior Body of clinoid sphenoid bone Sphenoid sinus Maxillary sinus Figure 2-19 This last coronal image of Exam 1, Figure 2-19, shows the anterior clinoids of the sphenoid bone along with the sphenoid sinuses, found in the body of the sphenoid bone. Little of the maxillary sinuses remain to be seen this far posteriorly. Axial Images Frontal Frontal bone sinus Compact bone Diploe Figure 2-20 This first axial image of Exam 1, Figure 2-20, demonstrates the frontal sinuses within the frontal bone. It also shows the unique construction of the cranial bones with diploe sandwiched between two layers of compact bone.
  14. 14. 80 Fundamentals of Sectional Anatomy Roof of orbit formed by horizontal portion of frontal bone Figure 2-21 Figure 2-21 shows how the roof of the orbits is formed by the horizontal portion of the frontal bone. Lateral mass of ethmoid bone Figure 2-22 On Figure 2-22, the lateral masses of the ethmoid bone are involved in forming the medial walls of the orbits.
  15. 15. CHAPTER 2 Face 81 Nasal bone Perpendicular plate of ethmoid Lens of eye bone Ethmoidal air Medial rectus cells muscle Optic nerve Lateral rectus muscle Figure 2-23 Seen on Figure 2-23 are the small, numerous, ethmoidal air cells found in the lateral masses or labrynths of the ethmoid bone. Identified are the nasal bones, as well as the perpendicular plate of the ethmoid bone forming the superior portion of the bony nasal septum. Although faintly visible, you can distinguish the medial and lateral rectus muscles, optic nerve, and lens of the eye. Bony nasal Lacrimal septum bone Ethmoidal Zygoma air cells Sphenoid sinus Figure 2-24 The bony nasal septum separates the two nasal fossae on Figure 2-24. Between the two orbits are the ethmoidal sinuses. Helping to form the medial walls of the orbits are the two lacrimal bones.The zygoma, involved in forming the lateral walls of the orbits, is shown.
  16. 16. 82 Fundamentals of Sectional Anatomy Maxillary bone Bony nasal septum Zygoma Maxillary sinus Sphenoid Nasal sinus concha Figure 2-25 Appearing for the first time in this series of images on Figure 2-25 are the maxillary sinuses and the maxillary bones. Also distinguishable are the sphenoidal sinuses, located in the body of the sphenoid bone beneath the sella turcica. On either side of the bony nasal septum are the conchae or turbinates.The prominent zygoma is seen in profile. Zygoma Maxillary Bony sinus nasal septum Sphenoid sinus Temporal Mastoid bone air cells Figure 2-26 On Figure 2-26, compare the size of the maxillary sinuses, the largest and the only ones present at birth, to the frontal, ethmoidal, and sphenoidal sinuses. In the mastoid region of the temporal bones are the mastoid air cells.
  17. 17. CHAPTER 2 Face 83 Maxillary sinus Figure 2-27 Figure 2-27 is at a lower level of the maxillary sinuses. Palatine processes of maxillary bone Palatine bone Mandible Figure 2-28 Figure 2-28, a thinner interslice gap compared to the previous images, is included because it demon- strates the hard palate. The hard palate or roof of the mouth is composed of the palatine processes (the horizontal portion of the maxillary bone) anteriorly and the two palatine bones posteriorly. Both should be united midline.
  18. 18. 84 Fundamentals of Sectional Anatomy Alveolar process of maxillary bone Mandible Figure 2-29 This last slice of Exam 1, Figure 2-29, shows the mandible, along with the alveolar process of the max- illary bones where the teeth insert.
  19. 19. CHAPTER 2 Face 85 Exam 2 Coronal Images Frontal Nasal bone sinus Perpendicular plate of Frontal process ethmoid of maxillary bone bone Figure 2-30 Seen on Figure 2-30 are the frontal sinuses within the frontal bone, the union of the frontal bone with the frontal processes of the maxillary bones, the nasal bones, and the perpendicular plate of the ethmoid bone. Frontal bone Crista galli Superior orbital Cribiform plate margin Lateral mass Ethmoidal of ethmoid sinuses bone Maxillary bone Figure 2-31 On Figure 2-31, the lateral masses of the ethmoid bone descending from the cribiform plate form the medial walls of the orbits. Extending superiorly from the cribiform plate is the crista galli and within the lateral masses are the ethmoid sinuses.The maxillary bones are just becoming visible.The superior orbital margin is formed by the frontal bone.
  20. 20. 86 Fundamentals of Sectional Anatomy Maxillary Cribiform bone plate Inferior Maxillary orbital sinus margin Alveolar process Figure 2-32 The inferior orbital margins are shown on Figure 2-32 formed by the maxillary bones medially and the two zygomatic bones laterally. The upper teeth are imbedded in the alveolar process of the maxillary bone. Just starting to appear are the maxillary sinuses. Superior rectus muscle Lateral rectus Optic nerve muscle Ethmoidal air sinus Superior nasal concha Zygomatic (malar) bone Maxillary sinus Middle nasal concha Vomer Inferior nasal concha Figure 2-33 On Figure 2-33 the conchae are seen dividing the nasal fossae into compartments. The size of the maxillary sinuses is appreciated. The vomer, making up the lower bony nasal septum, is identified as is the zygomatic prominence forming the cheeks bilaterally. Lastly, notice the rectus muscles and optic nerve.
  21. 21. CHAPTER 2 Face 87 Sphenoid bone Superior Maxillary Middle Conchae sinus Inferior Mentum of mandible Figure 2-34 Figure 2-34 has labeled the mentum or midpoint of the chin. Sphenoid sinus Middle concha Bony nasal septum Maxillary sinus Inferior concha Figure 2-35 On Figure 2-35, the nasal septum separates the two nasal fossae while the conchae divide them into compartments.
  22. 22. 88 Fundamentals of Sectional Anatomy Anterior clinoid of sphenoid Sphenoid bone sinus Figure 2-36 The anterior clinoids of the sphenoid bone are seen on Figure 2-36 along with the sphenoid sinuses in the body of the sphenoid bone beneath the sella turcica. Sphenoid Medial and sinus lateral pterygoid processes of sphenoid Figure 2-37 Figure 2-37 shows the sphenoid sinuses as well as the medial and lateral pterygoid processes of the sphenoid bone.
  23. 23. CHAPTER 2 Face 89 Mastoid air cells Temperomandibular Temperomandibular joint fossa Condyloid process of mandible Mandible Figure 2-38 Figure 2-38, the last image in this series, is a larger interslice gap compared to the previous images but is included to demonstrate the condyloid processes of the mandible articulating with the temporomandibular fossae of the temporal bones comprising the temporomandibular joints. Axial Images Frontal sinus Horizontal portion of frontal bone Mastoid air cells Figure 2-39 On Figure 2-39 you see the horizontal portion of the frontal bone forming the roof of the orbits. The frontal sinuses within the squamous portion of the frontal bone are also identified.
  24. 24. 90 Fundamentals of Sectional Anatomy Medial wall Lateral of orbit wall of orbit Anterior Posterior clinoid of clinoid of sphenoid sphenoid Figure 2-40 Figure 2-40 demonstrates the medial and lateral walls of the orbits taking shape. The anterior and posterior clinoids of the sphenoid bone are shown. Lacrimal bone Ethmoid air cells Lateral mass of ethmoid Perpendicular plate of ethmoid Lateral rectus muscle Medial rectus Sphenoid muscle sinus Mastoid air cells Figure 2-41 On Figure 2-41, the ethmoid and sphenoid sinuses are seen. Also identified is the medial wall of the orbit, formed by the lateral masses of the ethmoid bone and by the lacrimal bones. Labeled is the perpendicular plate of the ethmoid bone forming the superior portion of the bony nasal septum. Notice the medial and lateral rectus muscles and the mastoid air cells.
  25. 25. CHAPTER 2 Face 91 Nasal bone Lens of eye Ethmoid air cells Maxillary Sphenoid sinus sinus Figure 2-42 Three of the four sinuses are seen on Figure 2-42: the maxillary, sphenoid, and ethmoid. All com- municate with the nasal cavity. Also seen are the lens of the eyes and the nasal bones. Nasal bone Maxillary Zygoma sinus Foramen magnum Mastoid air cells Figure 2-43 Still apparent on Figure 2-43 are the nasal bones but more obvious now is the zygoma.The foramen magnum is seen along with the mastoid region of the temporal bones containing the mastoid air cells.
  26. 26. 92 Fundamentals of Sectional Anatomy Maxillary sinus Vomer Figure 2-44 Demonstrated on Figure 2-44 is the inferior bony nasal septum formed by the vomer. The fully formed maxillary sinuses are also seen. Palatine process of hard palate Figure 2-45 Figure 2-45, the last image shown in this exam, is a bigger interslice gap than the preceding images but is included to demonstrate the palatine process of the hard palate.
  27. 27. CHAPTER 2 Face 93 REVIEW QUESTIONS 10. Which of the following imaging planes will not demonstrate the lens of the eye? 1. The superior, middle, and inferior turbinates are part a. Coronal of the lateral masses of the ethmoid bone. b. Axial a. True c. Sagittal b. False d. They all will demonstrate the lens of the eye. 2. Which bone ends up disassociated in a tripod fracture? 11. On which imaging plane would you be able to see all a. Frontal four rectus muscles of the eye? b. Zygoma a. Sagittal c. Temporal b. Coronal d. Maxilla c. Axial d. All would be visible on all imaging planes. 3. Which bone forms the superior portion of the bony nasal septum? 12. Which paranasal sinus would appear first on CT a. Ethmoid images of the face done in a coronal plane arranged b. Sphenoid from anterior to posterior? c. Vomer a. Ethmoid d. Frontal bone b. Maxillary c. Frontal 4. What is the function of the conchae or turbinates in d. Sphenoid the nasal cavity? 13. The largest of the paranasal sinuses are the a. frontal. b. ethmoid. Match the different portions of the orbit with the bones c. sphenoid. composing them. d. maxillary. 5. Roof a. Maxillary, zygoma 14. The first paranasal sinuses to develop are the a. frontal. 6. Floor b. Ethmoid, lacrimal b. ethmoid. 7. Medial wall c. Zygoma, sphenoid c. maxillary. d. sphenoid. 8. Lateral wall d. Frontal bone 15. The function of the paranasal sinuses is 9. Which part of the orbit is involved in a blowout frac- ture? a. Roof . b. Lateral wall c. Medial wall d. Floor